Fix focus-gated needs-input flicker in live emulator query-response forwarding

[anutron]

Summary

• Focusing a Hera rail task's pane made its needs-input icon cycle moon → spinner → (?) → then bounce between (?) and moon roughly every second for as long as the pane stayed focused, with static/unresized/non-restarted content. Unfocusing settled it to moon and it stayed there.
• Root cause: the live PTY emulator's terminal-capability-query auto-answer forwarder (forwardEmulatorResponse, added by the recent OSC 10/11 color-query feature) delivered responses via Session.WriteInput, which stamps lastUserInput exactly like a real keystroke. idle-detection's clear-on-input logic (NeedsInputClear) reads that timestamp to decide "the user answered," so it falsely cleared a still-unanswered (?) flag every time the agent CLI's own periodic redraw re-triggered a capability-query response — which only happens on the currently-focused pane's live (non-discard) emulator, and recurs on roughly the same ~1s cadence as the app's needs-input detection ticker.
• Fix: route the forward through Session.WriteInputSystem instead — it advances only the work-cycle timestamp, mirroring the existing reliable-notify delivery pattern (internal/notify) that exists for exactly this reason. agentview.TerminalAdapter gained a WriteInputSystem method for this; real session types already implemented it, test fakes got a stub.
• The "settles to moon and stays there once unfocused" half of the report is not a separate bug — confirmed it's the pre-existing ClearedMarker stale-recandidacy suppression (BUG-063/BUG-067) legitimately recognizing unchanged content as already-cleared once no more live emulator exists to keep perturbing it. No change needed there; documented in the gotcha.

Process

• Routed through an OpenSpec change folder (fix-live-emulator-writeinput), archived atomically in this same PR (openspec/changes/archive/2026-08-22-fix-live-emulator-writeinput/, base spec terminal-rendering updated).
• Added a gotcha bullet to context/knowledge/gotchas/pty-terminal.md (and updated the index) documenting the invariant.

Test plan

• New/updated unit tests assert the delivery goes through WriteInputSystem, not WriteInput (TestTerminalPane_ForwardEmulatorResponse_ForwardsToSession, _DropsStaleOwner, the pre-existing TestTerminalPane_LiveEmulatorForwardsQueryResponseToSession).
• New end-to-end regression against a real *agent.Session proves LastUserInput stays zero while LastInput advances (TestTerminalPane_ForwardEmulatorResponse_DoesNotAdvanceLastUserInput).
• Verified all new/updated tests fail against the pre-fix code (temporarily reverted, confirmed red, restored).
• make pre-pr green except govulncheck (stdlib CVEs, advisory-only — CI itself runs this step with continue-on-error: true, same result on master).
• Full suite + -race on all touched packages green; two known pre-existing, unrelated local flakes confirmed independent of this change (internal/agent ARGUS_* env leakage in this sandbox, internal/selfupdate 1Password gpg-signing).

🤖 Generated with Claude Code

[github-actions]

Merging this branch changes the coverage (3 decrease, 3 increase)

Impacted Packages	Coverage Δ	🤖
github.com/drn/argus/internal/agent	89.88% (-0.02%)	👎
github.com/drn/argus/internal/api	87.00% (+0.01%)	👍
github.com/drn/argus/internal/apiclient	88.08% (+0.24%)	👍
github.com/drn/argus/internal/app/agentview	92.11% (-7.89%)	👎
github.com/drn/argus/internal/daemon	84.97% (ø)
github.com/drn/argus/internal/daemon/client	83.78% (+0.17%)	👍
github.com/drn/argus/internal/notify	90.60% (ø)
github.com/drn/argus/internal/tui	83.22% (-0.01%)	👎
github.com/drn/argus/internal/tui/hera	92.50% (ø)
github.com/drn/argus/internal/tui/terminal	96.12% (ø)

---

Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/drn/argus/internal/agent/iface.go	0.00% (ø)	0	0	0
github.com/drn/argus/internal/agent/needsinput.go	95.09% (ø)	265	252	13
github.com/drn/argus/internal/agent/session.go	95.98% (-0.10%)	199 (-5)	191 (-5)	8	👎
github.com/drn/argus/internal/api/handlers.go	87.43% (+0.05%)	732 (+3)	640 (+3)	92	👍
github.com/drn/argus/internal/api/push.go	94.88% (ø)	254	241	13
github.com/drn/argus/internal/apiclient/client.go	93.06% (+0.20%)	72 (+2)	67 (+2)	5	👍
github.com/drn/argus/internal/apiclient/session.go	82.43% (+0.43%)	148 (-2)	122 (-1)	26 (-1)	👍
github.com/drn/argus/internal/apiclient/settings.go	85.07% (ø)	67	57	10
github.com/drn/argus/internal/apiclient/terminal.go	82.46% (+0.97%)	57 (+3)	47 (+3)	10	👍
github.com/drn/argus/internal/app/agentview/terminal.go	0.00% (ø)	3 (+3)	0	3 (+3)
github.com/drn/argus/internal/daemon/client/handle.go	93.80% (+0.25%)	129 (+5)	121 (+5)	8	👍
github.com/drn/argus/internal/daemon/sessioncore.go	78.26% (ø)	161	126	35
github.com/drn/argus/internal/daemon/types.go	100.00% (ø)	1	1	0
github.com/drn/argus/internal/notify/service.go	90.91% (ø)	132	120	12
github.com/drn/argus/internal/notify/types.go	0.00% (ø)	0	0	0
github.com/drn/argus/internal/tui/app.go	78.71% (ø)	2752	2166	586
github.com/drn/argus/internal/tui/hera/panes.go	94.29% (ø)	140	132	8
github.com/drn/argus/internal/tui/heraactions.go	76.17% (ø)	579	441	138
github.com/drn/argus/internal/tui/terminal/terminalpane.go	96.31% (ø)	841	810	31

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.

Changed unit test files

• github.com/drn/argus/internal/agent/create_test.go
• github.com/drn/argus/internal/agent/session_race_test.go
• github.com/drn/argus/internal/agent/session_test.go
• github.com/drn/argus/internal/api/handlers_test.go
• github.com/drn/argus/internal/api/needsinput_test.go
• github.com/drn/argus/internal/api/notify_test.go
• github.com/drn/argus/internal/apiclient/client_test.go
• github.com/drn/argus/internal/apiclient/provider_test.go
• github.com/drn/argus/internal/daemon/client/client_test.go
• github.com/drn/argus/internal/daemon/client/handle_test.go
• github.com/drn/argus/internal/daemon/nudge_test.go
• github.com/drn/argus/internal/notify/service_test.go
• github.com/drn/argus/internal/tui/app_test.go
• github.com/drn/argus/internal/tui/bug031_test.go
• github.com/drn/argus/internal/tui/hera/panes_test.go
• github.com/drn/argus/internal/tui/heraactions_test.go
• github.com/drn/argus/internal/tui/terminal/forward_wheel_test.go
• github.com/drn/argus/internal/tui/terminal/terminalpane_test.go